As is well known in medical instrumentation technology, the radial loads generated in high speed drills are typically taken up by ball bearings. Preferably roller or needle bearings serve to take up these radial loads, but at high speed operations these bearings tend to deteriorate or burn out quickly and hence, the life of the drills or drill attachments utilizing the roller or needle bearings are limited and cannot attain the high rotational speeds that are often desired.
Many of drills utilized for medical applications are typically supported by ball bearings and utilize pneumatic driven motors that operate at relative high speeds. These drills rotatably support cutters and the like that when used in a medical procedure, the surgeon has the propensity to move the cutter sideways, which, obviously, imposes heavy, and sometimes severe, radial loads. Examples of these drills are the Black Max® and eMax™ manufactured by The Anspach Effort, Inc. the assignee of this patent application, and for further details of these types of drills reference should be made thereto and these models are incorporated herein by reference
Another example of bearings utilized for surgical instruments is disclosed and claimed in U.S. patent application Ser. No. 09/962,989 filed on Sep. 25, 2001 entitled “Bearings For Surgical Instruments” and assigned to the same assignee as this patent application, which is incorporated herein by reference. This patent application teaches the use of a journal bearing that replaces one of the bearings in the Micro Dissection Attachment (MDA) disclosed in this patent application. As taught in the aforementioned patent application, the journal bearing is made from a polymer of polyimide resin and graphite composition and is judiciously configured so that there are two points of contact of the mating surfaces. This bearing configuration allows for the miniaturizing of the MDA at the distal end so as to enhance the line of vision of the cutter for the surgeon to facilitate the procedure in surgery. The journal bearing of this teachings also enhances the wear characteristics of the MDA and has good characteristics for absorbing radial loads. Like the journal bearing as taught in the U.S. patent application Ser. No. 09/962,989, supra, the roller or needle bearing of this invention can be made sufficiently small so that it affords to the motor casing that is used as the handle the diameter of which is sufficiently small and affording to the surgeon a good feel for performing a surgical procedure, while enhancing the load characteristics of the instrument.
We have found that we can make diameter of the rollers of the needle/roller bearing of this invention substantially in the order of 0.0416 inch. Obviously, there are no limitation in the upper end of roller size of the bearing. Hence, for surgical instruments where the roller bearings only support radial loads, it is fundamentally important that the bearings sizes are small and factually, the smaller the bearing the better.
While ball bearings have been proven to be efficacious for many surgical instruments the needle or roller bearings are particularly efficacious for use in high speed drills and have advantages over the ball bearing when it is desirable to support the rotary shaft and take up the radial loads. This invention is intended to solve the problem noted in the above paragraphs by designing the needle/roller bearing so that alternate rollers of the bearing are made from metallic or ceramic material and the other alternate rollers are made from a non-metallic or ceramic material such as a plastic or a synthetic material. I have found that a stainless steel and a polyimide resin material or an alloy thereof combined with graphite material are particularly suited for these high speed rotary machines.
This invention contemplated utilizing the needle/roller bearing in these high speed surgical drills, as described above, and support the shaft in such a manner that the inner race, outer race and cage are eliminated. While the ball bearings described and claimed in U.S. patent application Ser. No. 10/153,368 filed on May 22, 2002, by Eddy Del Rio, entitled Ball Bearing are utilized for high speed drills and support the main drill shaft in the drill without the use of the inner race and outer race, it is believed that this arrangement of the needle/roller bearing with the absence of the inner race, outer race and cage of this invention has never been utilized heretofore.
As will be more evident in the description to follow, the needle/roller bearing of this invention is particularly efficacious when used in conjunction with a spherical thrust bearing. The invention lends itself to self-lubricate the rollers by mounting them in a sealed compartment containing a suitable grease or lubricant. This is true whether or not the thrust bearing is used in conjunction with the needle/roller bearing configuration.
We have found that bearings made in accordance with this invention affords the following characteristics although other characteristics may be realized:
1) The needle bearings are utilized without the races and hence, the overall envelope size is smaller in diameter than those utilizing races, enhancing the wear characteristics of the bearing;
2) the bearings are characterized as easy to manufacture, less expensive than heretofore known bearings, are maintenance free and are reliable and have a long operational life and particularly efficacious for high speed operation;
3) the material of the bearings can be any well known material, so long as alternate rollers are made from a metallic or ceramic material and the other alternate rollers are made from a non-metallic material or non-ceramic material;
4) pre-loading is not necessary;
5) the assembly and disassembly of the bearing are simplified in comparison to heretofore known needle bearings; and
6) misalignment of the rollers is obviated.
Moreover, tests have proven that drills manufactured utilizing bearings made in accordance with this invention have operated in high speeds that are typically utilized for these medical procedure without incurring any deficiencies.
The foregoing and other features of the present invention will become more apparent from the following description and accompanying drawings.